Apparatus for determining sulfur content of gaseous hydrocarbons



Aug. 27, 1968 J MAURlcE ET AL 3,399,038

APPARATUS FOR DETERMINING SULFUR CONTENT OF GASEOUS HYDROCARBONS Filed Oct. 11, 1963 2 Sheets-Sheet 1 INV E NTO R5 JHCQl/ES Maw/c5 .BfR/VHRD PFZ l/GFfLDER BERNARD Pnear BY C0Lrr5 Dwaar m fi m ATTORNEYS Aug. 27, 1968 J MAURICE ET AL APPARATUS FOR DETERMINING SULFUR CONTENT OF GASEOUS HYDROCARBONS Filed Oct. 11, 1963 2 Sheets-Sheet 2 5 e T mmero E U D 0 L if 1M D F E 2 $2 OIPAT m m F 0%40 ATTORNEYS United States Patent 3,399,038 APPARATUS FOR DETERMINING SULFUR CON- TENT OF GASEOUS HYDROCARBONS Jacques Maurice, Mourenx, Bernard Pflugfelder, Artix, Bernard Peyrot, Mourenx, and Colette Didelot, Pau, France, assignors to Societe Nationale des Petroles dAquitaine, Paris, France, a corporation of France Filed Oct. 11, 1963, Ser. No. 315,438 Claims priority, application France, Oct. 11, 1962, 912,058 2 Claims. (Cl. 23254) ABSTRACT OF THE DISCLOSURE Process and apparatus for measuring the sulphur content of various hydrocarbon gases containing trace amounts up to 30 p.p.m. of sulphur. The process entails the comparison of the electroconductivity of an electrolyte containing absorbed therein an oxidized portion of the hydrocarbon gas with the electroconductivity of an electrolyte containing oxidized gases obtained by first removing the sulphur content from a second portion of said hydrocarbon gas, oxidizing the substantially sulphur free gas and absorbing the oxidized gas in said electrolyte. The conductivity differences indicate the sulphur content. The apparatus of the invention comprises a burner with a plurality of gas inlets, first regulated means for supplying oxidizing gas to said burner, second regulated means for supplying said gas stream to said burner, a chamber filled with packing which communi cates with the outlet of said burner, heating means surrounding at least a portion of said chamber, cooling and sulphur dioxide absorption means communicating with the exit of said chamber and a conductivity cell connected to said cooling and absorption unit for measuring the electrical conductivity of electrolyte.

The present invention relates to a novel process for measuring the sulfur content of gaseous hydrocarbons. More particularly, the invention relates to a process for the continuous measurement of the total sulfur content of aliphatic and/or ethylenically unsaturated hydrocarbon gas streams such as natural gas. The invention also relates to an apparatus for carrying out the novel process.

Various hydrocarbons, especially natural gas, contain sulfur in different combined forms, e.-g. hydrogen sulfide, mercaptans, carbon oxysulfide, thiophene, etc. The conventional methods for measuring the sulfur content all require considerable time and are poorly adjustable to the continuous control of gas manufacture necessary for commercial purposes.

Therefore, an object of the present invention is to provide a process for the rapid and continuous measurement of the sulfur content of the gaseous hydrocarbon streams that render-s possible the immediate and accurate determination of the concentration of combined sulfur with sufficient precision from the industrial viewpoint for commercial utilization.

Another object of the invention is to provide a process for measuring the sulfur content of the hydrocarbon gas streams that can be applied to gas streams containing as low as trace amounts up to 30 ppm. of combined sulfur with sensitive and accurate detection.

Yet another object of the present invention is to provide a process and apparatus which provides a permanent record of the sulfur content of gas streams in an easily reproducible and convenient manner.

These objects and other attendant advantages of the present invention will become readily apparent as the same becomes better understood by reference to the following detailed description and drawings. It is to be understood that the following relates only to preferred embodiments of the invention and that equivalent reagents and apparatus may be substituted for those specifically disclosed.

The above objects are accomplished according to the invention by reacting the gas to be analyzed with oxygen so that all the sulfur present is converted to sulfur dioxide, absorbing the oxidized gas in an aqueous electrolyte, and measuring the increase of electrical conductivity of the electrolyte whereby the sulfur content is determined.

According to a preferred and important feature of the invention, the correct relative proportions of the hydrocarbon and oxygen are determined by adjusting the flow rates of. these streams so as to produce a blue flame on combustion.

According to another feature of the invention, a current of gas to be analyzed is periodically or continuously subjected to a treatment to eliminate sulfur compounds contained therein, whereafter the desulfurised gas is burned and the combustion products are absorbed into the same electrolyte solution used to absorb the S0 laden gas. Then the electrical conductivity is measured and the value found is used as a standard reference to be compared to the values of conductivity obtained with the absorbed burned crude gas not deprived of its sulfur compounds.

The sulfur-elimination treatment of the reference gas can be accomplished, for example, by passing a portion of this gas through a mass of one or more reagents capable of fixing the sulfur from the sulfur compounds present For this purpose it is possible to use any known desulfurising materials, but it is preferred to use those which do not react with the hydrocarbons of the gas themselves, and more especially do not oxidize them. In the case of the analysis of gases such as ethane, methane, ethylene or Lacq natural gas, excellent results are obtained with silver nitrate and potash as reagent for the elimination of the sulfur compounds.

The results of the analysis according to the invention, that is to say the values of the electrical conductivity of the solution after treatment with the products of combustion of the gas, can be continuously recorded in the form of a line traced on a graph. The reference values obtained with the gas deprived of its sulfur impurities constitute the zero line or base line of the graph. This base line can be traced continuously beside that of the analysis result by continuously feeding a portion of the gas to be analyzed into a sulfur-elimination apparatus, followed by a combustion apparatus parallel with that serving for the analysis of the crude gas. The base line 1 s discontinuous, and appears intermittently on the graph, 1f the measurement of the conductivity of the gas deprived of sulfur is effected only periodically. It has been found that in the application of the invention to the control of the sulfur in natural gas, such periodical determinations of the base line are entirely sufficient. They can be conducted, for example, every hour.

The apparatus according to the invention 'for measuring the sulfur content of a gaseous hydrocarbon comprises means for the supply (which can be regulated) of a stream of gas to be analyzed and of oxygen or oxygen containing gas, e.g. air, connected respectively to the entries of a burner, a chamber filled with a packing after the burner, a refrigerating unit, the entry of which communicates with the exit of the chamber, and a cell for the measurement of the electrical conductivity of an electrolyte, connected to the said refrigerating unit.

A preferred form of the apparatus includes a device, for the elimination of the sulfur from the hydrocarbon,

which can be fed from the means for supply of th gas to be analyzed, in such manner that it is possible to supply the burner either with crude gas or with gas deprived of its sulfur impurities.

The apparatus preferably includes a devic for recording the value characterising the electrical conductivity to be measured.

In order to illustrate the invention ther will be described hereinafter by way of non-limitative example an apparatus which has given good results in the continuous measurement of the sulfur content of hydrocarbons such as methane and ethylene.

In the accompanying drawings:

FIGURE 1 is 'a schematic diagram of the apparatus of the invention.

FIGURE 2 is a horizontal diagrammatic view of the body of the blow pipe.

FIGURE 3 is a horizontal diagrammatic view of the burner nozzle of the blow pipe.

FIGURE 4 is a horizontal diagrammatic view of the quartz tube.

FIGURE 5 is a diagrammatic view of the elongated connector between the quartz tube and the refrigerating unit, and

FIGURE 6 is a vertical diagrammatic view of the refrigerating unit.

In FIGURE 1 the gaseous hydrocarbon to be controlled and analyzed is fed into the conduit below valve 1. Threeway valves 3 and 4 permit the passage of this feed stream through absorber 5 or allow the direct feed to flow meter 6. Absorber 5 contains several layers of fixed bed sulfureliminating material. At 5a a layer of glass wool is in turn covered with a layer 5b of grains of anhydrous calcium chloride mixed with glass rings, substantially in the proportions of two parts calcium chloride to one part glass rings. At 5c the intermediate layer is covered with a granular mixture comprising two parts of silver nitrate to one part of potassium hydroxide. The flow of gas is metered at 6 by a flow meter preferably a rotameter such as NO. FM. 1043B of the Manostat Corporation. Before entering blower pipe 8, the gas flows through three-way valve 7 which permits venting the gas to the atmosphere if this is necessary.

The body of the blow pipe 8 contains the burner or nozzle 9, and it communicates further with a flow meter 10 connected by a conduit 21 to an oxygen supply. The blow pipe 8 is fitted, by conical grinding, to the entry of a quartz tube 11 which is heated by being enclosed in an electric oven 12. At its downstream end the tube 11 communicates with a thermally insulated extension 13 kept I at about 150 C. by means of an electric heating resistance.

The outlet of the extension 13 is connected to the upper inlet of the refrigerating unit 14 which is cooled by water circulation indicated diagrammatically by arrows.

At 15 there are represented diagrammatically the principal elements of a known conductivity cell of the Wosthotf type. The flow of the refrigerating un it 14 terminates at the measuring cell 22. The degasifier of the cell is at 24 and the decanter at 23. A recording apparatus automatically records the signal of conductivity measured. The tube of the decanter 23 dips into the water of the constant-level tank 20, supplied by the water issuing from the refrigerating unit 14.

16 and 17 are conical flasks for smoothing the flow of the hydrocarbon under analysis through rotameter 6. 18 designates a mercury valve serving as regulator of this same flow. The tube 18t dips into the mercury above which water is situated. The excess hydrocarbon is vented to the atmosphere through the pipe 18a. The flow of the gas at 6 is regulated to the desired value by manipulating the clipping tube 181 in the column of mercury.

The mercury and water valve 19 regularizes the pres sure of the oxygen in quartz tube 11 and in degasifier 24. The conduit 21 is connected on the one hand to a cylinder of oxygen, on the other to the entry of flow meter 10 and by its descending branch to regulator 19.

The body of blow pipe 8, represented in greater detail in FIGURE 2, comprises at its axial entry a spherical male ground portion 8a and at the exit a conical ground portion 8b matching the corresponding grinding of tube 11. The lateral entry for the oxygen, terminates with a spherical female grinding 8d. The axial pipe contained in the blow pipe terminates by a grinding 8c which matches the corresponding entry grinding 9c of the nozzle 9 represented in FIGURE 3.

The blow pipe nozzle 9 comprises a calibrated quartz capillary tube 9a, the downstream end of which. has a circular groove 9b and the end of the nozzle comprises platinum wires 9d.

In FIGURE 4 is a detail of the quartz tube 11 which constitutes the chamber following the blow pipe 9. In the part of this tube situated inside the electric oven 12 there is first disposed at 11a a platinum wire wound into a ball; next comes a charge of quartz 11b ground into fine grains, generally not exceeding 2 mm.; at 11c there are placed coarser fragments of quartz. The relativ dimensions of the nozzle of the blow pipe and of the tube 11 are such that the end of the flame of the blow pipe nozzle 9 is at least 10 mm. from the platinum wire 11a.

In FIGURE 5 the neck of the glass extension 13 is shown to be surrounded by a heating wire 26.

In the electrolyte inlet 27 of the refrigerating unit there is provided a constriction 28. The neck 29 at the entry of the refrigerating unit is as short as possible.

An apparatus constructed in accordance with the foregoing description possessed the following characteristics the dimensions being indicated in millimetres.

Absorber tube 5, diameter: 30, length: 700, height of 5b: 100, height of 50: 600.

Rotameter 6, used with a sapphire ball, measurement range 0.2 to 16 litres per hour. This range is 0.4 to litres per hour for the rotameter 10.

Quartz tube 11, diameter: 10, length: 500.

Tubular electrical oven 12, external diameter: 110, internal: 20, length: 250, supplied at 220 volts with a regulator permitting maintaining the temperature at about 650 C.

Blow pipe nozzle 9, total length: 240, length of the calibrated capillary 9a; 160, external diameter of the latter: 6, internal 0.2.

Refrigerating unit, height: 150, diameter of internal tube: 6, constriction at 28 of diameter: 1.

In order to place the apparatus in operation, the electric oven 12 and the heating resistance 26 are switched on. When they have reached the temperatures of 650 C. and C. respectively, the flow meter 10 is connected. The Wosthotf apparatus 15 is turned on after the oxygen supply has been opened long enough for slight bubbling to occur at 19.

Then the flow meter 10 is connected and the dipping part of the tube 21 is regulated so that the liquid in the degasifier 24 always remains visible. Then oxygen is permitted to pass for 5 minutes, while ensuring that the three-way valve 7 is in position to direct the gases solely to atmosphere. At the same time the valve 2 is opened and the hydrocarbon gas stream is regulated and smoothed by means of the flow meter 6 and the conical flasks 16 and 17.

The valves 3 and 4 are placed in the position to direct the gas passing solely through the column 5. The tube 181 is raised so as to dip only'into water.

Then the gas to be analyzed is passed until bubbles are obtained in 18 and the valve 7 isplaced in communi' cation with the flow meter 6 and the blow pipe nozzle 9. The height of the tube 18! is regulated to bring the flow at 6 to the desired value.

If all these operations have been correctly carried out, the ignition of the gas at the end of the blow pipe nozzle 9 takes place spontaneously. The fiame must have a H2804 l1'l l. H202 V01.) ml 1 Wosthoif Docen wetting agent ml 2 H O (Q.S.p.) litres This electrolyte is supplied to the refrigerating unit by means of the hand pump of the Wosthoff device. In order to ensure that the internal tube of the refrigerating unit 14 is completely wetted, the pump is operated gently.

In normal operation the combustion must be complete. If the flame should become smokey, or if tars should be deposited in the extension 13 and the refrigerating unit 14, it is necessary immediately to extinguish the flame by directing the gas to atmosphere through the valve 7.

The recording apparatus 25 is connected five minutes after the starting of the apparatus. Normally it is stabilized after fifteen minutes of operation. The base line which corresponds to a blank test is situated to the left of the graph and is a vertical straight line.

After a blank test of one hour, or the time necessary for the recording of a base line of for example about 1 cm., the valves 3 and 4 are placed in such manner that the gas to be analyzed passes through the flow meter and arrives at the blow pipe nozzle 9, without passing through the absorber 5. If one operates too slowly, the flame is extinguished for a few seconds and then automatically relights itself. If there are sulfur compounds in the gas, after about 2 minutes, one observes a displacement of the base line of the graph towards the right. The measurement is effected for an hour, after which the valves 3 and 4 are operated afresh in order to carry out again a blank test with gas which has passed through the absorber 5. It is then appropriate to let the flame extinguish itself and to cause its relighting only after 5 seconds.

This operation should be repeated preferably every hour in order to determine the position of the base line which might possibly be subject to a slight drift, of which account must be taken. Furthermore, the possible formation of a black deposit on the platinum wires at the end of the blow pipe nozzle is thus prevented.

The distance between the base line corresponding to a blank test and the line traced in the course of the measurement is proportional to the sulfur content of the gas to be analyzed.

The described process and apparatus have given good industrial results of the sulfur compound concentration, especially of ethylene and methane, for sulfur contents ranging between trace amounts and 40 p.p.m. In the tests with gases containing predetermined sulfur proportions, the determinations of sulfur content by the process of the invention have given results the relative deviations of which in relation to theory generally do not exceed 10%.

Such results are summarlzed below:

Hydrocarbons S p.p.m. S p.p.m. Relative,

introduce found percent From the above, it is apparent that the present invention provides a single, accurate commercially acceptable method for the continuous determination of sulfur content of hydrocarbon gas streams.

What is claimed is:

1. A gas analysis system for measuring the sulfur content of a gaseous hydrocarbon stream having sulfur impurities, comprising: an inlet line for the gases to be analyzed for sulfur content, a burner communicating with said inlet line, an oxygen supply line connected to said burner, a combustion chamber in communication with said burner, a gas absorber connected to receive gases from said combustion chamber, means for passing electrolyte solution through said gas absorber for removal of S0 from the burned gases, means for measuring the electrical conductivity of the electrolyte from the absorber, a branch line selectively connectable into the inlet line, means in said branch line for removal of sulfur from hydrocarbon gases, means for selectively connecting said branch line into the system so that desulfurized gases and sulfur containing gases can be selectively passed in sequence through the combustion and analyzing means, and means for comparing the electrical conductivity of the absorption electrolyte through which the burned sulfur containing gases have been passed with the electrical conductivity of the absorption electrolyte solution through which the burned desulfurized gases have been passed to thereby provide an accurate measure of the sulfur content of the gases.

2. A gas analysis system as defined in claim 1 wherein the means in said branch line for removal of sulfur from hydrocarbon gases comprises a chamber containing a granular mixture of silver nitrate and potassium hydroxide.

References Cited UNITED STATES PATENTS 9/1960 Clauss. 7/1964 Hoel et al 23-253 OTHER REFERENCES MORRIS O. WOLK, Primary Examiner.

R. M. REESE, Assistant Examiner. 

